1. Field of the Invention
The present invention relates to a digital video cassette recorder (VCR), and more particularly to an apparatus for and a method of interleaving/deinterleaving for a digital VCR which can effectively correct errors occurring in recording or reproduction of compressed data and improve error correction capability, especially in variable speed reproduction.
2. Description of the Prior Art
The errors occurring in recording and reproduction with a digital VCR may be classified as random errors and burst errors. Random errors independently occur in digital signal lines due to additive noise during signal processing, and burst error is successive error occurring with respect to a bit stream of transmission data under the influence of tape condition, and so on. Burst error can be corrected by being replaced with random errors through an interleaving/deinterleaving process.
A conventional interleaving apparatus for a digital VCR, as shown in FIG. 1, includes outer coder 1 for performing outer coding with respect to an input compressed data stream and successively outputting the data stream with an outer code symbol added thereto, first sector array memory 2 for successively storing the data outputted from outer coder 1, and inner coder 3 for reading the data stored in first sector array memory 2 in an order different from that in storing the data to first sector array memory 2, performing inner coding, outputting and recording the data with inner code symbol added thereto on a tape via a head. The interleaving apparatus is also provided with inner decoder 4 for decoding only data having the inner code symbol among the data reproduced from the tape, detecting errors in the data and performing interleaving with respect to such detected errors, second sector array memory 5 for distributively storing the interleaved data from inner decoder 4, and outer decoder 6 for reading out data from second sector array memory 5 in an order different from that in writing the data and performing decoding with respect to data having the outer code symbol to correct the errors.
In the conventional interleaving apparatus constructed as above, when the compressed data stream as shown in FIG. 2A is inputted, outer coder 1 performs outer coding in a vertical direction with respect to a series of symbols of the input data as shown in FIG. 2B and outputs data having the outer code symbol. Then, a redundancy is added to the data having the outer code symbol as shown in FIG. 2C and the redundancy-added data is stored in first sector array memory 2 in the order shown in FIG. 2D.
Inner coder 3 reads out the data from first sector array memory 2 in an order different from that in storing the data and performs interleaving to add the inner code symbol to the data. Accordingly, the order of the data is changed, being different from that of the input data, causing a burst error to be replaced by random errors. The data stream interleaved as described above is then inner-coded by inner coder 3, with the result that strong error correction coding (ECC) is performed.
Inner decoder 4 decodes the data having the inner code symbol among the data having the inner and outer code symbols reproduced from the tape and detects and corrects the errors. That is, in correcting the errors, inner decoder 4 performs interleaving with respect to the errors which exist beyond its capability and distributively stores the interleaved data still having errors in second sector array memory 5. Outer decoder 6 performs outer decoding with respect to the data stored in second sector array memory 5 to correct the remaining errors, and thereby various kinds of errors occurring in reproduction in a digital VCR can be corrected and prevented.
The conventional apparatus as described above thus provides a strong capability to correct various errors occurring in reproduction of data and is suitable for use in a digital VCR for professional purposes.
However, in a home digital VCR, such an elaborate apparatus for strong error correction cannot be used due to a limitation of recording frequency bandwidth and high costs.
Also, in high speed play such as a picture search mode, the VCR head, as shown in FIGS. 4A to 4C, passes across various tape tracks and the head trace region in a track, as well as the size of a sector array memory in the conventional apparatus, is inversely proportional to the degree of high speed.
Practically, the VCR head in high speed play has a nonlinear trace as shown in FIG. 4C, and this causes the maximum interleaving region for ECC to be further restricted in comparison to the linear head trace. Also, in high speed play, the head continually passes the track portion of the same position due to the restricted interleaving region, and the image data of the same picture portion is extracted. Accordingly, in order to obtain the image data of other picture portions, data allocation for rearranging the data recording position is required.
Further, when a signal is recorded on a tape track by the conventional apparatus as shown in FIG. 10A, a redundancy is added to the signal, utilizing a two-dimensional Reed-Solomon code for correcting various kinds of burst and random errors. Thus, in normal reproduction of the signal, the decoding array is fully occupied with information data and the 2-dimensional Reed-Solomon decoding can be performed.
However, in a special reproduction such as a high speed play, only a portion of the track can be traced, and thus the decoding array is partially occupied with information data and only one-dimensional error decoding can be used, causing the confidence in correcting the errors to deteriorate.
Meanwhile, the data segments reproduced by the conventional apparatus are classified into complete segments and incomplete segments, and the data segment is composed of slices which are the variable unit in which the image data and other information are compressed and compacted. Accordingly, as shown in FIG. 15, several slices may exist in the K-th segment while a slice may exist over two segments as shown in (k+1)-th segment.
Such slices may be performed with variable length coding (VLC) or compressed at different rates in encoding a high quality image or a normal image. Thus, the lengths of the respective compressed data streams may appear to be different from one another, even though the respective image information of the same amount are compressed. Accordingly, in order to perfectly perform the variable length decoding (VLD) in a decoder, a complete bit stream should be reproduced in the unit of slice.
According to the conventional apparatus, however, groups of complete and incomplete segments are placed in the detected area as shown in FIG. 16 when the reproduced data stream has been deinterleaved in variable speed play. If the slices, being the unit of data compaction, exist over incomplete segments excluding the group of complete segments, such slices in the incomplete segments will be of no use, inviting data loss.